Federer, 33, claimed his sixth Western and Southern Open title in Cincinnati on Sunday with victory over Spain's David Ferrer, the last key tune-up event for the U.S. Open.
The result was good enough for him to become the third man to qualify for the eight-player event, behind Novak Djokovic and Rafael Nadal, the world numbers one and two.
"It's always one of the big goals I set myself at the beginning of the season," Federer, a six-time Finals winner, said in a statement.
"It's always an absolute honour being part of the best eight. Getting a chance to win an extra trophy at the end of the season - which is so prestigious, one of the biggest ones we have in the game and one I've done so well at - is a great feeling."
The 17-times grand slam champion battled in 2013, winning just one title, suffering a shock second-round exit at Wimbledon and dropping outside the world top four for the first time in a decade.
Now back at number three, he has confounded those who said his career was coming to an end, going down in five sets to Djokovic in the Wimbledon final and winning three titles.
"Returning to the season finale is something I've been a part of since 2002, so to do it again is a privilege and I will try to play my very best there," he added.
"I hope I can save some of my best for last."
(Reporting by Josh Reich; Editing by John O'Brien)
